The primary mission of the Rochester Developmental Psychopathology Study is to clarify the relationship between environmental and constitutional factors in the development of psychiatric disability. To this end, mothers have been described with regard to psychiatric diagnosis; chronicity of illness; social competency; anxiety level; and attitudes toward pregnancy. Similarly, their children have been evaluated along selected dimensions of behavior that reflect central nervous system activity and individual differences in social and intellectual performance. Undertaken at five different age-periods, i.e., pre-natal; birth; four-month; 12-months and 30-months, this longitudinal research program has begun to describe the relative contributions of environmental and constitutional factors in the etiology of serious mental disorder.